Carotid sinus baroreceptors evoke activity of the sympathetic system as a whole, affecting a multiplicity of organs and not only the cardiovascular system. Studies of hepato-portal receptors have shown that excitation by specific substances (NaCl, glucose) can elicit hypothalamic neuron responses. Responses of the hypothalamus is to a high degree conditioned by circadian rhythms within the cellular population concerned. The study of factors which determine sensitivities of responses in the central neurons will be continued.